This invention belongs to the field of mechanics, specifically to the area of clutches and, in particular, to clutches between concentric shafts. The purpose of this invention is to provide an original, simple, reliable, and low-cost clutch design.
There are many different types of clutches. The most common are friction clutches that help to shift the gearbox of an automobile. However, these clutch systems are far too expensive for simple applications, making it necessary to develop alternatives designs to migrate to lower cost solutions with fewer components, that are easy to manufacture and produce, and stands aggressive or uncommon environments. For example, clutches of the type that operate submerged in some type of hydraulic or electromagnetic fluid, and should withstand the attack of chemicals, sediments, dirt, the presence of foreign objects, different fluid densities, particles traveling by the fluid, and even the presence of organisms in the fluid. In these environments, a friction clutch would not work properly or the specific application requires a different torque level.
Thus, this invention can provide a clutch system for concentric shafts that are not required to transmit high levels of torque. Preferably, the shafts would be placed in a vertical position because the action of gravity is desirable for the proper operation of the proposed system. They would be totally or partially submerged in some type of fluid, for example, a small fish tank pump that requires at least two different pumping speeds, depending on the fluid level inside; or industrial agitators where chemicals are blended in huge tanks that require at least two different mixing speeds or that require that the paddles spin at the same or at different speeds, depending on the level of the fluid or the physicochemical characteristics of the process. Other possible applications may be the treatment of wastewater separation of solids, fans, turbines, etc.
Examples of some efforts to achieve the requirements described on the paragraph above are described next. U.S. Pat. No. 3,557,580 to Racenis describes a transmission system of an automatic washing machine with a peculiar clutch. Said patent describes a grooved shaft driven at one end, and having a splined surface on which the central portion of a reel of female splined matching is placed; in one of its faces it has bulges or teeth arranged to engage a shaft, which will drive it; said reel is moved along the axis through a connecting rod. U.S. Pat. No. 2,609,697 to Ruscoe describes a similar device: an internal motor shaft that transmits high speeds in only one direction; an external shaft connected to a transmission that delivers oscillatory motion at low speed; a system consisting of a clutch and a reel with serrated upper and lower faces that moves along the axis over the internal motor shaft. At its highest position, the reel engages the teeth of the upper face to those set under the “T” or “hat” at the end of the internal motor shaft. Said reel has a bell structure that slides from its upper section along the axis over the grooves of the third shaft that is driven. When the reel is at its lowest position, it engages the teeth set over the lower face to those set on the upper face of the cogwheel of the oscillating outer motor shaft, delivering oscillating motion to the third collinear driven shaft.
Top loading automatic washing machines represent a very interesting and natural application for this invention, because these devices use several types of clutches. An agitator or a propeller agitates the water, so that fluid and soap (washing liquor) passes through the fibers of the fabric and to create friction among clothing and remove dirt with the washing liquor. After this, the washing liquor is removed, the clothes are rinsed and centrifuged. For these operations, the cloth-containing basket needs to spin at high velocity, which is not the action done by the agitator because it just oscillates at a lower speed but with a higher torque. Given these characteristics, this invention is ideal for this application; considering and compared to the complex clutch systems or multiple component systems that make them unreliable, expensive, and difficult to manufacture or assemble.
There are several approaches to employ similar systems on top loading automatic washing machines as described by the U.S. Pat. No. 2,665,576 to Thiele, it discloses a clutch system of two fixed gears arranged over a motor shaft, it spins at the same speed as the shaft; and a flotation assembly that includes the agitator and the basket, a feature that is not very desirable in current top loading domestic washing machines, because this configuration tangles the clothes. When the flotation assembly floats due to the presence of the washing liquor, the female cogs set inside the body of the agitator engage the fixed cogs, thus receiving energy from the motor shaft. This system has the inconvenience of not using a pair of concentric shafts, and shows a complicated system of bands and other clutches in order to carry out the different washing operations. This situation is additional to the great space that the flotation chambers require to provide lift and move the entire tub including the clothes and the agitator in the presence of a certain level of water.
Another contribution to the state of the art is Patent GB915997 of Kovosmalt, Narodny Podnik that describes a clutch for a top loading automatic washing machine with a peculiar feature. For the spinning cycle, it is not necessary to remove the water from the liquid reservoir tub (container), instead of that, the basket is raised by means of a spring and blocking systems that secure the basket, both in its raised position and when it lays on the bottom of the reservoir tub. This washing machine has an agitator that spins independently from the washing basket. The clutch system is comprised of a dented hub that engages some handles set over the second outer shaft on which the upper end of the agitator is also set on a square arranged for that purpose. Said dented hub transmits power from the second outer shaft to the washing basket on the spinning cycle; when the basket is raised, the dented hub falls and engages the basket to the second outer shaft. This has the disadvantage of having to raise and lower the basket to engage the clutch, as well as raising the washing basket to be able to spin its contents which, according to the configuration of modern washing machines desirable.
Another text worthy of study is U.S. Pat. No. 5,651,277 to Richardson, which describes a clutch for an automatic washing machine that comprises a floating cone with a dented lower part and some splines arranged in the periphery; said splines engage some ribs arranged for this purpose inside the agitator so that the agitator and the floating cone spin in unison. The lower part of the cone is dented in order to engage with some ribs in a radial arrangement at the bottom of the basket; this way the agitator is set on a motor shaft connected to the electric engine, the shafts pass across the reservoir tub and basket. The basket has a bearing arrangement on the hub with a coaxial arrangement on the motor shaft. In a first scenario, the reservoir tub has a set minimum level of liquid and the floating cone rises separating itself from the bottom of the basket, allowing the agitation or washing action inside the basket. The next scenario is when there is no washing liquid and the floating cone lays on the bottom of the basket due to the action of gravity; the energy from the engine passes through the motor shaft, the agitator, the floating cone and, at the end, it reaches the bottom of the basket, thereby achieving the spinning action. However, this system has a series of drawbacks: The action of the clutch takes place in a wet environment or in contact with water which is associated to the problems described below. To work correctly, the system needs to drain the basket completely; if the basket is not properly drained, the floating cone will not complete its clutch stroke. Another noticeable problem shows on the ribs set at the bottom of the basket, which are ideal places for the buildup of scale, fluff, impurities, and detergent residues, which, in time, could increase the width of the ribs and stop the floating cone from engaging correctly. Besides, thin or small garments such as handkerchiefs, socks, diapers, cloth, etc, can be pulled and get stuck under the agitator aided by the ribs and holes, obstructing the zone where the clutch action takes place, so the floating cone will not be able to engage correctly to the bottom of the basket. This creates an unhealthy condition because, being in a place that cannot be seen, the user is not aware of all the fluff sediments, dirt and the clothes that tend to accumulate in the ribs creating a growing media for bacteria. The user is unable to remove the impurities because he/she can hardly see them or even imagine this is taking place under the agitator or propeller; which creates a paradox because washing machines are supposed to be hygienic devices which purpose is to clean clothes or garments that go through a washing cycle inside said devices; the design of a washing machine should foresee and address these inconveniences and not allow the buildup of foreign objects, fluff, fibers, sediments, scale or dirt in general. Therefore, we can conclude that said ribs are undesirable, because they complicate the design and manufacture of the basket, they are not hygienic, they damage the cloths, and they make the system fail after a while. Additionally, it is evident that the floating cone has serious drawbacks as well; one is the design itself, because by having an open flotation chamber, some lift is lost due to the buildup or adherence of sediments to the air chamber. The lift will be poor because, according to our analysis, it will only have enough lift to rise, but it can be assumed that the turbulence present in the zone during the agitation action will cause the floating cone to descend, engaging the tub for brief periods, due to the decrease of the air volume inside the air chamber; which, while open, allows the exchange of airflow for a liquid flow, this combined with the buildup of scale or sediments in time will increase the weight, which will reduce lift.
Another interesting document is U.S. Pat. No. 6,634,193 to Lee, et al., disclosing a clutch located between a solid motor shaft and an outer hollow propelled shaft. The internal shaft is splined on its exposed part or outside the outer hollow shaft. The latter also has a type of spline on its upper end. The floating assembly travels along the axis on the solid motor shaft (internal), since the floating assembly has two splines; the first one with a narrower diameter is located on the upper part of the floating assembly, big enough to travel along the axis over the solid motor shaft. The second spline is located just in the lower part of the first spline, where it is necessary to increase the diameter to accommodate the outer hollow shaft (propelled); thus, when the floating assembly settles down due to the action gravity, it engages the lower spline of greater diameter to the spline on the end of the outer shaft. Now the internal and external shafts spin in unison. So far the invention seems to work properly, but the problem lays in how to obtain a “dry” clutch, which means that the part or parts that perform the clutch action must not be in contact with the water, to prevent foreign objects from housing in there (as was the case with Richardson). Probably, thinking about this possibility, a hollow shaft or a sheathing protruding from the center of the propeller was procured. This sheathing is formed downwards and covers the central part of the floating assembly, forming some kind of cover that almost seals the bottom of the floating assembly, and because the flotation chambers are located at the level where the clutch engages they surround the rest of the floater. This design prevents foreign objects from housing in the clutch. However it allows the buildup of residues, due to the dirt carried by water, water hardness, high contents of soap and other chemicals, which over time build up between the jacket of the propeller and the floating assembly, thereby preventing a good performance. If we consider for a moment that the user may inadvertently pour an extraordinary volume of soap, saturating the mix of liquid and soap, a phenomenon known in the art as “sudsing”, the creation of an extraordinary volume of foam will occur. This foam has certain characteristics, like bubbles of small size, high contents of soap allow the creation of stiffer structures with a higher air concentration. This type of foam tends to form or get inside small spaces and, at best, only leaves traces or sediments, but at worst it can stop objects in motion or even support the weight of a light object. Thus the discussed patent fails to solve this problem by not addressing it properly, because supposing that the user doses the washing liquid with a large amount of soap and creates the foam described above, the foam will get between the jacket or cover protruding from the center and downward the agitator or propeller and the center of the floating assembly. A possible scenario is that it just builds up sediments, but another scenario is that the “sudsing” effect is created, preventing the proper operation of the clutch, thus causing an undesirable failure that is difficult to repair. Another inconvenience of this design is the use of splines, because machining these splines require a high degree of precision, since an uncontrolled variation could cause, in a first hypothetical scenario, a lack of sufficient space between the pieces and a “loose” fitting that is necessary for the system to disengage the clutch without losing any lift, otherwise causing a loss of efficiency and reliability in the operation of the clutch, or a “snuggly” fit (not loose), or in the worst case, a “clenched” fit. This is critical because when the space between the parts is reduced until they interfere with each other, the system may get stuck and fails. Another hypothetical scenario is having an assembly that is “loose” beyond tolerated limits, which means that the clearance between them is too much, so, when the torque is transmitted there would not be enough contact surfaces between the faces of the splines, thereby causing mechanical engagement failure, and may even wear the splines. The use of splines and the little space of the analyzed system can cause friction between its parts, reducing the freedom of motion and reducing lift; also, during the washing cycle there is evaporation of the water and capillarity. In the first situation, the evaporated water transports salts from the washing liquor, which adhere to the surface of the spline of the shaft and the spline of the floating assembly, thickening their surface and reducing the clearance, thereby provoking unwanted contact between the parts, increasing the coefficient of friction, reducing lift or causing the system to stall. In the second situation, the capillarity can cause buildup of sediments in the clutch zone, the base cylinder and the sheathing (the agitator protrusion), thus affecting the operation of the system. Also we must point out that the floating assembly is not designed to have a bottom lid that would allow catching air efficiently, permitting the entrance of fluid into the flotation chamber, thus reducing the volume of air inside the chamber and causing a reduction in lift, combined with the possibility of building up sediments or foreign objects, making the floating assembly heavier in time. Another drawback of this system is located in the seal or O-ring used to connect the propeller to the motor shaft because it could, in time, allow air leakages and the access of water to the clutch zone or dry chamber, thereby affecting sliding of the pieces because the washing liquid can rust the splines, increasing the friction between the floating cone and the shaft. We must point out that when the washing liquid enters the air chamber it carries sediment fibers and other undesirable objects into the compartment, causing the system to get stuck and fail.
Given the inconveniences described above, we provide an original design for concentric shafts, by avoiding the structural and design problems of prior efforts, and producing an economic clutch, easy to manufacture, repair and maintain, reliable and resistant to chemical attack; that is not affected by the buildup of sediments and that doesn't allow access of or housing foreign elements in the clutch zone. With these considerations in mind the invention hereof will be described below.